(a) Field of the Invention
The present invention relates to an interconnection system in a semiconductor device and, more particularly, to a new metallic interconnection system having a Ti.sub.2 N compound. The present invention also relates to a method for manufacturing such a semiconductor device.
(b) Description of the Related Art
Finer pattern for an interconnection system, as well as higher-integration and miniaturization for device elements, has been intensively developed in semiconductor devices such as DRAMs. For the finer pattern of the interconnection system, it is proposed that silicide on polysilicon (polycide) and tungsten silicide be used for gate electrodes or word lines and bit lines, respectively, in a DRAM. In this structure, polycide is generally used for contacts between bit lines and source/drain regions of MOSFETs constituting memory cells as well as for contacts for capacitors.
With the advance of further higher integration and miniaturization, there arises the problem in that the resistivity of the tungsten silicide or polycide tends to decrease the operational speed of the semiconductor device, and accordingly, a new conductive material is desired having a lower resistivity and a higher stability at a higher temperature.
Patent Publication JP-A-7(1995)-155775 proposes that titanium nitride (TiN) be used in a single conductive layer as a high-melting compound instead of tungsten silicide and polyicide and that gate electrodes or interconnection systems in MISFETs be formed also by TiN. In this publication, however, instability of TiN during a heat treatment is not recited.
Patent Publication JP-A-59(1984)-39049 proposes that a nitride, boride or carbide of a transition metal such as titanium (Ti), zirconium (Zr) and vanadium (V) be used for an interconnection system in a semiconductor device. It is also proposed therein that, since the nitride of a transition metal exhibits a higher resistivity in a direct contact with a semiconductor layer, the contact resistance be reduced by interposing a pure transition metal between the semiconductor layer and the nitride.
In JP-A-59-39049, it is not mentioned that the nitride of transition metal has a larger resistivity than the pure transition metal to increase the overall resistance. In addition, only TiN is recited as an example of nitrides and the instability of TiN during a heat treatment is not recited therein.
An article in "Thin Solid Films", 60(1979) pp. 237-247 by W. J. Garceau et al., teaches that a TiN layer interposed between Ti and Pt is effective as a diffusion barrier for preventing formation of Ti--Pt intermetallic compounds. It is also recited that the resistivity of TiN changes with the function of nitrogen content: the resistivity increases up to about 100 .mu..OMEGA..multidot.cm with the increase of nitrogen between zero and 35 at. % of nitrogen and, with a discontinuity, dramatically decreases down to about 40 .mu..OMEGA..multidot.cm with a small amount of increase in nitrogen content above 35 at. %.
In the article as mentioned above, TiN is not recited as an underlying layer for the interconnection system, and the thermal stability of TiN after the dramatic change in the resistivity is not mentioned therein.